Electronic engine control device, vehicle equipped with electronic engine control device, and electronic engine control method

ABSTRACT

On the premise that a target torque of an engine is equal to 0, that observed catalyst temperature is in a specified temperature range causing deterioration of the catalyst, and that the engine runs idle without a fuel cut regardless of fulfillment of preset fuel cut conditions, the control procedure of the invention determines whether a predetermined engine stop condition is fulfilled (step S 300 ). Upon fulfillment of the predetermined engine stop condition, the control procedure subsequently determines whether a high load is applied to an exhaust catalyst (step S 320 ). The engine runs idle (step S 310 ) when a high load is applied to the exhaust catalyst. The relatively low-temperature exhaust gas from the engine in the idling state forcibly cools down the exhaust catalyst. This prevents the exhaust catalyst from being kept at high temperature. When a low load is applied to the exhaust catalyst at step S 320 , on the other hand, the engine is stopped (step S 330 ). The stop of the engine cuts off the air flow through the exhaust catalyst. The exhaust catalyst is thus not exposed to the lean exhaust atmosphere and does not significantly deteriorate even at high temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic engine control device and a vehicle equipped with the electronic engine control device, as well as a corresponding electronic engine control method.

2. Description of the Prior Art

A known vehicle control device temporarily stops fuel injection to improve the fuel consumption rate, when a throttle valve is in full closed position and the engine rotation speed is not lower than a preset level (for example, when the vehicle runs down a slope without the driver's depression of an accelerator pedal). Rotation of the engine under the fuel cut keeps the air flow through the engine and thereby makes the lean exhaust atmosphere. An exhaust catalyst significantly deteriorates, when being exposed to the lean exhaust atmosphere at high temperature. One proposed technique disclosed in Japanese Patent Laid-Open Gazette No. 10-196433 prohibits the fuel cut when either an inlet temperature or an outlet temperature of the exhaust catalyst exceeds a predetermined high level, so as to prevent significant deterioration of the exhaust gas. Another proposed vehicle control device disclosed in Japanese Patent Laid-Open Gazette No. 9-154205 stops the engine according to the driving conditions of the vehicle and automatically restarts the engine, in order to improve the fuel consumption rate.

The vehicle may fall into the driving state that requires a stop of the engine under catalyst deterioration control executed to prevent significant deterioration of the exhaust catalyst. In such cases, the engine may not be stopped with preference to the catalyst deterioration control to prevent significant deterioration of the exhaust catalyst. This prohibition of the engine stop, however, leads to the low fuel consumption rate. The automatic engine stop during a drive of the vehicle or at a short stop of the vehicle, for example, at a traffic light, is one of the advantageous characteristics of hybrid vehicles equipped with both an engine and a motor as the power source and of vehicles under idle stop control. Especially in such vehicles, it is demanded to effectuate the automatic engine stop simultaneously with prevention of significant deterioration of the exhaust catalyst.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electronic engine control device and corresponding method that ensure a good balance between prevention of significant deterioration of an exhaust catalyst and improved fuel consumption rate by stop of the engine. The object of the invention is also to provide a vehicle equipped with the electronic engine control device.

In order to attain at least part of the above and the other related objects, the present invention is directed to an electronic engine control device that controls an engine. The electronic engine control device includes: the engine that converts combustion energy produced by combustion of an air fuel mixture or a mixture of the air and a fuel into kinetic energy; an exhaust catalyst that purifies an exhaust gas from the engine; a fuel injection unit that injects the fuel into the engine; a catalyst deterioration control module that controls the fuel injection unit to keep fuel injection and idles the engine regardless of fulfillment of a preset fuel cut condition, when temperature of the exhaust catalyst is in a specified temperature range causing deterioration of the catalyst; and an engine stop restart control module that stops the engine upon fulfillment of a preset engine stop condition and restarts the engine upon subsequent fulfillment of a preset engine restart condition. Upon fulfillment of the preset engine stop condition during idling of the engine by the catalyst deterioration control module, the engine stop restart control module idles the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst. In this electronic engine control device, the level of the load applied to the exhaust catalyst may be set high in a preset high load range, while being set low out of the preset high load range.

The present invention is also directed to an electronic engine control device that controls an engine. The electronic engine control device includes: the engine that converts combustion energy produced by combustion of an air fuel mixture or a mixture of the air and a fuel into kinetic energy; an exhaust catalyst that purifies an exhaust gas from the engine; and an engine stop restart control module that stops the engine upon fulfillment of a preset engine stop condition and restarts the engine upon subsequent fulfillment of a preset engine restart condition. Upon fulfillment of the preset engine stop condition, the engine stop restart control module idles the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst.

In one preferable embodiment of the electronic engine control device of the invention, the engine stop restart control module may determine a level of load applied to the exhaust catalyst according to thermal energy of the exhaust gas. It is especially preferable that the thermal energy of the exhaust gas is integrated over a time period to determine the level of load applied to the exhaust catalyst. The load level applied to the exhaust catalyst significantly depends upon the thermal energy of the exhaust gas. It is thus desirable to determine the load level applied to the exhaust catalyst according to the thermal energy of the exhaust gas. Here the terminology ‘thermal energy of the exhaust gas’ is not restricted to its literal meaning but may represent a parameter closely correlated to the thermal energy of the exhaust gas, for example, a parameter varying with a variation in thermal energy of the exhaust gas. In the structure of integrating the thermal energy of the exhaust gas over the time period to determine the level of load applied to the exhaust catalyst, one preferable procedure computes the thermal energy of the exhaust gas for every preset time interval and integrates the computed thermal energy over a time period between an ignition-on time and the current time to determine the load level applied to the exhaust catalyst.

The engine stop restart control module may utilize at least either of a temperature and a flow rate of the exhaust gas as the thermal energy of the exhaust gas. The load level applied to the exhaust catalyst significantly depends upon the temperature and the flow rate of the exhaust gas. It is thus desirable to determine the load level applied to the exhaust catalyst according to the temperature and the flow rate of the exhaust gas. Here the terminology ‘temperature of the exhaust gas’ is not restricted to its literal meaning but may represent a parameter other than the temperature of the exhaust gas that is used for estimation of the temperature of the exhaust gas. Similarly the terminology ‘flow rate of the exhaust gas’ is not restricted to its literal meaning but may represent a parameter other than the flow rate of the exhaust gas that is used for estimation of the flow rate of the exhaust gas. The flow rate of the exhaust gas running through the exhaust catalyst may be an intake air flow introduced into the engine. The air introduced into the engine is mixed with a fuel to an air-fuel mixture. The exhaust gas is produced through combustion of this air-fuel mixture.

In the electronic engine control device of the invention, the preset engine stop condition preferably includes a condition that a current vehicle speed is in a preset engine stop permission vehicle speed range. For example, the engine stop permission vehicle speed range is set to be not higher than several ten km/h (for example, not higher than 65 km/h) in the electronic engine control device mounted on a hybrid vehicle, while being set to almost zero (for example, not higher than 5 km/h) in the electronic engine control device mounted on a vehicle under idle stop control.

In another preferable embodiment of the invention, the electronic engine control device further includes a three shaft-type power input-output unit that determines a power input from and output to residual one shaft based on powers input from and output to any two shafts among three shafts, that is, an output shaft of the engine, a connection shaft connected to a first motor generator, and a drive shaft of a vehicle connected to a second motor generator. The engine is idled by setting a rotational resistance of a rotor in the first motor generator to zero for an idle of the connection shaft.

The present invention is also directed to a vehicle equipped with any of the electronic engine control devices described above. Thus, the vehicle of the invention idles the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst, upon fulfillment of the preset engine stop condition during idling of the engine by the catalyst deterioration control.

The present invention is further directed to an electronic engine control method that controls an engine. The electronic engine control method includes the steps of: (a) keeping fuel injection and idling the engine regardless of fulfillment of a preset fuel cut condition, when temperature of an exhaust catalyst, which purifies an exhaust gas from the engine, is in a specified temperature range causing deterioration of the catalyst; (b) upon fulfillment of a preset engine stop condition during idling of the engine in step (a), idling the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst; and (c) restarting the engine upon fulfillment of a preset engine restart condition after stop of the engine in step (b).

The present invention is further directed to an electronic engine control method that controls an engine. The electronic engine control method includes the steps of: (a) upon fulfillment of a preset engine stop condition, idling the engine under application of a high load to an exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst; and (b) restarting the engine upon fulfillment of a preset engine restart condition after stop of the engine in step (a)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the configuration of a hybrid vehicle 10 in one embodiment of the invention;

FIG. 2 schematically shows the structure of an engine 20;

FIG. 3 is a flowchart showing a hybrid control routine;

FIG. 4 shows an example of torque demand setting map;

FIG. 5 shows a process of setting the optimum drive point;

FIG. 6 is an example of an alignment chart for determining the rotation speed of a shaft;

FIG. 7 is a flowchart showing an engine control routine;

FIG. 8 schematically illustrates the configuration of a hybrid vehicle in one modified structure; and

FIG. 9 schematically illustrates the configuration of a hybrid vehicle in another modified structure.

BEST MODES OF CARRYING OUT THE INVENTION

FIG. 1 schematically illustrates the configuration of a hybrid vehicle 10 in one embodiment of the invention. FIG. 2 schematically shows the structure of an engine 20 mounted on the hybrid vehicle 10 of the embodiment.

As illustrated in FIG. 1, the hybrid vehicle 10 includes the engine 20 that converts combustion energy generated by combustion of a fuel into kinetic energy, an engine electronic control unit (engine ECU) 50 that controls the whole engine system, a three shaft-type power distribution integration mechanism 30 that is linked to a crankshaft 27 or an output shaft of the engine 20, motors MG1 and MG2 that are connected to the power distribution integration mechanism 30 and are capable of generating electric power, and a motor electronic control unit (motor ECU) 14 that controls power generation and actuation of the motors MG1 and MG2. The hybrid vehicle 10 also includes a battery 45 that transmits electric power to and from the motors MG1 and MG2, a battery electronic control unit (battery ECU) 46 that monitors the charging conditions of the battery 45, a drive shaft 17 that is linked via a chain belt 15 to a shaft connecting with the power distribution integration mechanism 30, and a hybrid electronic control unit (hybrid ECU) 70 that controls the whole hybrid system. The drive shaft 17 is connected to drive wheels 19, 19 via a differential gear 18. As shown in FIG. 2, the hybrid vehicle 10 further includes a catalytic converter 60 that is located downstream the engine 20 and works to purify the exhaust gas, and a catalyst temperature sensor 63 that measures the temperature of an exhaust catalyst 61 packed in the catalytic converter 60.

The engine 20 is an internal combustion engine that consumes a hydrocarbon fuel, such as gasoline, to output power. The engine 20 receives a supply of the air cleaned by an air cleaner 21 and ingested via a throttle valve 22, while receiving a supply of gasoline injected by an injector 23 (fuel injection unit). The supplies of the intake air and the injected gasoline are mixed to an air-fuel mixture, which is introduced into a combustion chamber via an intake valve 24 and is ignited for explosive combustion with an electric spark of an ignition plug 25. Reciprocating motions of a piston 26 by means of combustion energy of the explosive combustion are converted into kinetic energy of rotating the crankshaft 27. A crank angle sensor 67 is attached to the crankshaft 27 to output a pulse at every crank angle of 10° CA. The throttle valve 22 varies its inclination angle (opening) relative to the cross section of an intake conduit to regulate the air flow passing through the intake conduit. The opening of the throttle valve 22 is electrically varied by a throttle motor 22 a. The opening of the throttle valve 22 is output from a throttle position sensor 22 b to the engine ECU 50. The exhaust gas from the engine 20 goes through an exhaust conduit 64 and the catalytic converter 60 for removal of toxic components included in the exhaust gas, that is, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), and is discharged to the outside air. An exhaust gas temperature sensor 65 is attached to the exhaust conduit 64 to measure the temperature of the exhaust gas flowing through the exhaust conduit 64.

The catalytic converter 60 is connected to the exhaust conduit 64 and is filled with the exhaust catalyst 61. The catalyst temperature sensor 63 measures the temperature of the catalyst bed of the exhaust catalyst 61. An NTC-characteristic thermistor is adopted for the catalyst temperature sensor 63 to measure the high temperature of the exhaust gas even close to 1000° C. The three-way catalyst used as the exhaust catalyst 61 includes an oxidation catalyst, such as platinum (Pt) or palladium (Pd), a reduction catalyst, such as rhodium (Rh), and a co-catalyst, such as ceria (CeO₂). The oxidation catalyst converts CO and HC included in the exhaust gas into water (H₂O) and carbon dioxide (CO₂), while the reduction catalyst converts NOx included in the exhaust gas to nitrogen (N₂) and oxygen (O₂). When the air-fuel ratio of the air-fuel mixture is in a window range close to the stoichiometric air-fuel ratio, the adsorption and decomposition of NOx by the reduction catalyst well balance the oxidation of HC and CO with oxidizing components produced in the process of adsorption and decomposition. Namely the three-way catalyst has high conversion rates for all the toxic components HC, CO, and NOx in this window range. The valence of cerium (Ce) in ceria (CeO₂) reversibly changes between trivalence and tetravalence. CeO₂ has a change in valence of Ce from trivalence to tetravalence and absorbs and stores oxygen from the exhaust gas in the lean exhaust atmosphere, while having a change in valence of Ce from tetravalence to trivalence and releasing oxygen to the exhaust gas in the rich exhaust atmosphere. This effectively prevents a significant change of the atmosphere in the vicinity of the oxidation catalyst and the reduction catalyst and thus expands the window range. As is well known in the art, exposure of the exhaust catalyst 61 to the lean exhaust atmosphere at high temperature (for example, 750° C. or higher) lowers the conversion power of the exhaust catalyst 61. This may partly be ascribed to the particle growth and a resulting decrease in surface area of the oxidation catalyst and the reduction catalyst.

The engine ECU 50 is constructed as a microprocessor including a CPU 52, a ROM 54 that stores various processing programs, a RAM 56 that temporarily stores data, and input and output ports (not shown). The engine ECU 50 receives diverse signals representing the present conditions of the engine 20 from various sensors via its input port. For example, the engine ECU 50 receives, via its input port, an air intake flow of the engine 20 from an air flow meter 28, a throttle opening from the throttle position sensor 22 b, catalyst temperature sent from a catalyst temperature sensor 63, exhaust gas temperature measured by an exhaust gas temperature sensor 65, and a pulse signal from the crank angle sensor 67. The engine ECU 50 outputs diversity of drive signals and control signals to drive and control the engine 20 via its output port. For example, the engine ECU 50 outputs, via its output port, drive signals to the throttle motor 22 a, drive signals to the injector 12. 23, and control signals to an ignition coil 29 integrated with an igniter for igniting the spark plug 25. The engine ECU 50 is electrically connected with the hybrid ECU 70 and receives control signals from the hybrid ECU 70 to drive and control the engine 20, while outputting data regarding the driving conditions of the engine 20 to the hybrid ECU 70 according to the requirements. The engine ECU 50 corresponds to a catalyst deterioration control module and an engine stop restart control module of the present invention.

The power distribution integration mechanism 30 includes a sun gear 31 that is linked to the motor MG1, a ring gear 32 that is linked to the motor MG2, multiple pinion gears 33 that engage with the sun gear 31 and with the ring gear 32, and a carrier 34 that is connected to the crankshaft 27 of the engine 20 and holds the multiple pinion gears 33 to allow both their revolutions and their rotations on their axes. The power distribution integration mechanism 30 accordingly forms a planetary gear mechanism of the sun gear 31, the ring gear 32, and the carrier 34 as rotational elements of differential motions. When the motor MG1 functions as a generator, the power distribution integration mechanism 30 distributes the output power of the engine 20 into the motor MG1 and the drive shaft 17 corresponding to a gear ratio of the sun gear 31 and the ring gear 32. When the motor MG2 functions as a motor, on the other hand, the power distribution integration mechanism 30 integrates the output power of the engine 20 with the output power of the motor MG2 and outputs the integrated power to the drive shaft 17.

The motors MG1 and MG2 are constructed as known synchronous motor generators that may be actuated both as a generator and as a motor. The motors MG1 and MG2 transmit electric powers to and from the battery 45 via inverters 41 and 42. Power lines 58 connecting the battery 45 with the inverters 41 and 42 are structured as common positive bus and negative bus shared by the inverters 41 and 42. Such connection enables electric power generated by one of the motors MG1 and MG2 to be consumed by the other motor MG2 or MG1. The battery 45 may thus be charged with surplus electric power generated by either of the motors MG1 and MG2, while being discharged to supplement insufficient electric power of either of the motors MG1 and MG2. Both the motors MG1 and MG2 are driven and controlled by the motor ECU 14. The motor ECU 14 receives signals required for driving and controlling the motors MG1 and MG2, for example, signals representing rotational positions of rotors in the motors MG1 and MG2 from rotational position detection sensors 43 and 44 and signals representing phase currents to be applied to the motors MG1 and MG2 from electric current sensors (not shown). The motor ECU 14 outputs switching control signals to the inverters 41 and 42. The motor ECU 14 executes a rotation speed computation routine (not shown) to calculate rotation speeds Nm1 and Nm2 of the respective rotors in the motors MG1 and MG2 from the input signals of the rotational position detection sensors 43 and 44. The calculated rotation speeds Nm1 and Nm2 are respectively equivalent to a rotation speed Ns of a sun gear shaft 31 a and a rotation speed Nr of a ring gear shaft 32 a, since the motor MG1 is linked to the sun gear 31 and the motor MG2 is linked to the ring gear 32. The motor ECU 14 establishes communication with the hybrid ECU 70 and receives control signals from the hybrid ECU 70 to drive and control the motors MG1 and MG2, while outputting data regarding the driving conditions of the motors MG1 and MG2 to the hybrid ECU 70 according to the requirements.

The battery 45 used in this embodiment is a nickel hydride battery and functions to supply electric power to the motors MG1 and MG2 and accumulate the regenerative energy from the motors MG1 and MG2 during deceleration in the form of electric power. The battery ECU 46 receives signals required for management of the battery 45, for example, an inter-terminal voltage from a voltage sensor (not shown) located between terminals of the battery 45, a charge-discharge electric current from an electric current sensor (not shown) located in a power line connecting with an output terminal of the battery 45, and a battery temperature from a temperature sensor (not shown) attached to the battery 45. The battery ECU 46 outputs data regarding the conditions of the battery 45 to the hybrid ECU 70 by communication according to the requirements. For management of the battery 45, the battery ECU 46 computes a remaining charge level or current state of charge (SOC) of the battery 45 from an integration of the charge-discharge electric current measured by the electric current sensor and the inter-terminal voltage measured by the voltage sensor.

The hybrid ECU 70 is constructed as a microprocessor including a CPU 72, a ROM 74 that stores processing programs, a RAM 76 that temporarily stores data, and a non-illustrated input-output port. The hybrid ECU 70 receives various inputs via the input port: a gearshift position SP from a gearshift position sensor 82 that detects the current position of a gearshift lever 81, an accelerator opening AP from an accelerator pedal position sensor 84 that measures a step-on amount of an accelerator pedal 83, a brake pedal position BP from a brake pedal position sensor 86 that measures a step-on amount of a brake pedal 85, and a vehicle speed V from a vehicle speed sensor 88. The hybrid ECU 70 communicates with the engine ECU 50 and the motor ECU 14. The hybrid ECU computes state of charge (SOC) of the battery 45 from an accumulated value of the charge discharge electric current measured by a non-illustrated electric current sensor. The hybrid ECU 70 corresponds to a power demand determination module.

The following describes a hybrid control routine executed by the hybrid ECU 70 and an engine control routine executed by the engine ECU 50 in the hybrid vehicle 10 of the embodiment having the configuration discussed above.

The hybrid control routine executed by the hybrid ECU 70 is described first with reference to the flowchart of FIG. 3. The hybrid control routine is carried out repeatedly at preset timings. In the hybrid control routine, the CPU 72 of the hybrid ECU 70 first inputs signals required for control, that is, the accelerator opening AP, the vehicle speed V, and the remaining charge or state of charge (SOC) of the battery 45 computed by the battery ECU 46 (step S100) and sets a torque demand Tr* and a power demand Pr* to be output to the ring gear shaft 32 a, based on the input accelerator opening AP and the input vehicle speed V (step S110). The concrete procedure of the embodiment for setting the power demand Pr* stores in advance variations in torque demand Tr* against the accelerator opening AP and the vehicle speed V as a torque demand setting map in the ROM 74 of the hybrid ECU 70, reads the torque demand Tr* corresponding to the given accelerator opening AP and the given vehicle speed V from the torque demand setting map, and computes the power demand Pr* as the product of the torque demand Tr* and the rotation speed Nr of the ring gear shaft 32 a (equal to the product of the vehicle speed V and a conversion factor r). One example of the torque demand setting map is shown in FIG. 4.

The CPU 72 subsequently sets a charge discharge power demand Pb* of the battery 45 (positive values for charging and negative values for discharging) (step S120). The charge-discharge power demand Pb* of the battery 45 is typically set to keep the SOC of the battery 45 in an adequate range (for example, 60 to 70%). The power demand Pr* and the charge-discharge power demand Pb* are summed up as an engine power demand Pe* to be output from the engine 20 (step S130).

The engine power demand Pe* of the engine 20 is compared with a preset minimum power level Pref (step S140). The minimum power level Pref is determined empirically on the ground that the output power level of the engine 20 below the minimum power level Pref lowers the total system efficiency of the hybrid vehicle 10. When the engine power demand Pe* is not lower than the preset minimum power level Pref at step S140, an optimum drive point of ensuring the most efficient operation of the engine 20 is set to a target torque Te* and a target rotation speed Ne* of the engine 20, among possible drive points of the engine 20 for output of the engine power demand Pe* (drive points defined by the combinations of the torque and the rotation speed) (step S150). FIG. 5 shows a process of setting the optimum drive point of ensuring the most efficient operation of the engine 20 among the possible drive points for output of the engine power demand Pe* to the target torque Te* and the target rotation speed Ne*. A curve A represents an optimum engine operation line, and a curve B represents a constant power curve of the engine power demand Pe*. The power is expressed by the product of the torque and the rotation speed. The constant power curve B accordingly has an inverse proportional profile. As clearly understood from this graph, the operation of the engine 20 at the optimum drive point, which is the intersection of the optimum engine operation line A and the constant power curve B of the engine power demand Pe*, ensures the efficient output of the engine power demand Pe* from the engine 20. The concrete procedure of the embodiment experimentally or otherwise specifies in advance a variation in optimum drive point against the engine power demand Pe* and stores the variation as a map in the ROM 74 of the hybrid ECU 70. The rotation speed and the torque at an optimum drive point corresponding to the given engine power demand Pe* are read from the map and are set to the target rotation speed Ne* and the target torque Te*.

After setting the target torque Te* and the target rotation speed Ne*, the CPU 72 calculates a target rotation speed Nm1* of the motor MG1 from the target rotation speed Ne* of the engine 20, the rotation speed Nr of the ring gear shaft 32 a, and a gear ratio ρ (=the number of teeth of the sun gear 31/the number of teeth of the ring gear 32) of the power distribution integration mechanism 30 according to Equation (1) given below (step S160). The CPU 72 also computes a target torque Tm1* of the motor MG1 from the target torque Te* of the engine 20 and the gear ratio ρ of the power distribution integration mechanism 30 according to Equation (2) given below, while computing a target torque Tm2* of the motor MG2 from the target torque Te* of the engine 20, the gear ratio ρ of the power distribution integration mechanism 30, and the torque demand Tr* according to Equation (3) given below (step S170): Nm 1*=(1+ρ)×Ne*/ρ−Nr/ρ  (1) Tm 1*=−Te*×ρ/(1+ρ)  (2) Tm 2*=Tr*−Te*×ρ/(1+ρ)  (3)

FIG. 6 is an alignment chart with the rotation speeds of the respective rotating shafts as the ordinate and the gear ratio of the respective gears as the abscissa. The crankshaft 27 or carrier shaft (expressed by C) is located at a position of internally dividing the interval between the two end positions of the sun gear shaft 31 a (expressed by S) and the ring gear shaft 32 a (expressed by R) at 1 to ρ. The rotation speeds Ns, Nc, and Nr are plotted corresponding to the respective positions S, C, and R. The power distribution integration mechanism 30 is the planetary gear mechanism as mentioned above, so that these three plots are aligned. This line is called the collinear line. The use of this collinear line automatically determines the rotation speed of a residual shaft based on the preset rotation speeds of any two among the three rotating shafts. The rotation speed Nr of the ring gear shaft 32 a (equivalent to the rotation speed Nm2 of the motor MG2) depends on the vehicle speed V. Determination of the rotation speed Nc of the carrier shaft (equivalent to the rotation speed Ne of the engine 20) thus automatically sets the rotation speed Ns of the sun gear shaft 31 a (equivalent to the rotation speed Nm1 of the motor MG1) by the proportional division as shown by Equation (1) given above. Substitution of the torques applied on the respective rotating shafts by forces acting on the collinear line proves that the collinear line is balanced as a rigid body. Here it is assumed that a torque Te applied on the crankshaft 27 of the engine 20 is expressed by an upward vector at the position C relative to the collinear line and that a torque Tr applied on the ring gear shaft 32 a is expressed by a downward vector at the position R. The direction of each vector represents the acting direction of the torque. Based on the distribution law of the force applied on the rigid body, the torque Te is distributed to both the end positions S and R. A distributive torque Tes at the position S is expressed by an upward vector having a magnitude of Te×ρ/(1+ρ), whereas a distributive torque Ter at the position R is expressed by an upward vector having a magnitude of Te×1/(1+ρ). The collinear line is balanced as the rigid body under such conditions. The torque Tm1 to be applied to the motor MG1 accordingly has the same magnitude as but the opposite direction to those of the distributive torque Tes. The torque Tm2 to be applied to the motor MG2 is equal to a difference between the torque Tr and the distributive torque Ter.

After setting the target rotation speed Ne* and the target torque Te* of the engine 20, the target rotation speed Nm1* and the target torque Tm1* of the motor MG1, and the target torque Tm2* of the motor MG2, the CPU 72 sends these target values to the engine ECU 50 and the motor ECU 14 (step S190) and terminates the hybrid control routine. The engine ECU 50 and the motor ECU 14 respectively drive and control the engine 20 and the motors MG1 and MG2, based on the received target values. The drive control of the engine ECU 50 sets an air flow required for the engine 20 to rotate at the target rotation speed Ne* and output the target torque Te*, computes an amount of intake air per rotation of the engine 20 from the required air flow, and controls the actuator 22 a to rotate the throttle valve 22 and regulate the throttle opening corresponding to the computed amount of intake air. The drive control of the engine ECU 50 also calculates a required amount of fuel injection or a fuel injection time by the injector 23 from a preset target air-fuel ratio (for example, stoichiometric air-fuel ratio) corresponding to the computed amount of intake air, opens the valve of the injector 23 to allow fuel injection for the computed fuel injection time, and applies a high-voltage to the ignition coil 29 to cause the ignition plug 25 to generate a spark and ignite the air-fuel mixture ingested by the intake valve 24. The piston 26 moves up and down by means of the generated combustion energy. The vertical motions of the piston 26 are converted to rotational motions of the crankshaft 27.

When the engine power demand Pe* of the engine 20 is lower than the preset minimum power level Pref at step S140, on the other hand, the CPU 72 sets both the target torque Te* of the engine 20 and the target torque Tm1* of the motor MG1 to zero, the target rotation speed Ne* of the engine 20 to an idle rotation speed Ni, and the target torque Tm2* of the motor MG2 to the torque demand Tr* (step S180). The CPU 72 then sends the target torque Te* and the target rotation speed Ne* of the engine 20, the target torque Tm1* of the motor MG1, and the target torque Tm2* of the motor MG2 to the engine ECU 50 and the motor ECU 14 (step S190), and terminates the hybrid control routine. Setting of the target torque Te* of the engine 20 to zero leads to setting of the engine power demand Pe* to zero. Setting of the target torque Tm1* of the motor MG1 to zero causes no-load operation (idling) of the motor MG1, while setting of the target torque Te* of the engine 20 to zero causes no-load operation (idling) of the engine 20. The target torque Tr* of the ring gear shaft 32 a is thus all supplied by the motor MG2. Regulation of the inverter 41 to set the rotational resistance of the rotor in the motor MG1 to zero attains the no-load operation of the motor MG1. The idle rotation speed Ni is appropriately varied according to the driving conditions of the engine 20 by the engine ECU 50.

An engine control routine executed by the engine ECU 50 is described with reference to the flowchart of FIG. 7. The following description is on the assumption that the target torque Te* of the engine 20 sent from the hybrid ECU 70 is equal to 0, that the observed catalyst temperature sent from the catalyst temperature sensor 63 is in a specified temperature range causing deterioration of the catalyst, and that the engine 20 is driven with no load or runs idle without a fuel cut regardless of fulfillment of preset fuel cut conditions. Namely the engine control routine is executed under catalyst deterioration control. The fuel cut conditions are that the rotation speed Ne of the engine 20 is higher than a preset reference level Nref and that the accelerator opening AP is equal to zero. The fuel cut conditions are fulfilled, for example, when the hybrid vehicle 10 runs down a slope. The catalyst deterioration temperature range is an empirically specified high temperature range having a high potential for deterioration of the oxidation catalyst and the reduction catalyst in the exhaust catalyst 61 exposed to the lean exhaust atmosphere (for example, a range of not lower than 750° C.).

When this engine control routine starts under catalyst deterioration control, the engine ECU 50 first determines whether a predetermined stop condition of the engine 20 is fulfilled (step S300). In this embodiment, the stop condition of the engine 20 is that the vehicle speed V input from the vehicle speed sensor 88 is not higher than an engine stop permission level. The engine stop permission level may be determined to prevent the rotation speed of the motor MG1 from reaching its upper limit speed at a stop of the engine 20 (that is, while the rotation speed Ne of the engine 20 or the rotation speed Nc of the carrier shaft is equal to zero). The engine stop permission level is set to, for example, 65 km/h. Upon no fulfillment of the stop condition of the engine 20 at step S300, that is, when the stop condition of the engine 20 is not satisfied under the fuel cut conditions and under the condition of the observed catalyst temperature in the specified temperature range causing deterioration of the catalyst, the engine ECU 50 idles the engine 20 to prevent significant deterioration of the exhaust catalyst 61 (step S310) and immediately exits from this engine control routine. The engine 20 is accordingly rotated at an idle rotation speed Ni. The exhaust catalyst 61 is thus not exposed to the lean exhaust atmosphere and does not significantly deteriorate even at high temperature. The exhaust gas during idling of the engine 20 has relative low temperature (for example, 500 to 600° C.). The flow of the relatively low-temperature exhaust gas through the exhaust catalyst 61 lowers the temperature of the exhaust catalyst 61.

Upon fulfillment of the stop condition of the engine 20 at step S300, on the other hand, the engine ECU 50 subsequently determines whether a load applied to the exhaust catalyst 61 is in a preset high load range (step S320). The load applied to the exhaust catalyst 61 represents thermal energy (amount of heat) of the exhaust gas applied to the exhaust catalyst 61 and is calculated from a difference between the catalyst temperature and the exhaust gas temperature, the exhaust gas flow, and the time elapsed. The catalyst temperature is measured by the catalyst temperature sensor 63, and the exhaust gas temperature is measured by the exhaust gas temperature sensor 65 attached to the exhaust conduit 64. The exhaust gas flow represents the flow rate of the exhaust gas discharged from the engine 20 and is closely correlated to the air intake flow introduced into the engine 20. The air intake flow is thus used as the exhaust gas flow in this embodiment. The air intake flow may be measured directly by the mass flow system, may be estimated from the pressure of an intake conduit and the engine rotation speed by the speed density system, or may be estimated from the throttle opening and the engine rotation speed by the throttle speed system. These systems are all known in the art and are thus not explained in detail. The control procedure of this embodiment adopts the throttle speed system to read an air intake flow in the ordinary state from a two-dimensional map of the throttle opening and the engine rotation speed as parameters and determine the actual air intake flow through required corrections of the air intake flow in the ordinary state. The control procedure of this embodiment determines the difference between the observed catalyst temperature and the observed exhaust gas temperature and the exhaust gas flow at every preset time interval, computes the thermal energy applied to the exhaust catalyst 61 (positive energy when the catalyst temperature <the exhaust temperature and negative energy when the catalyst temperature> the exhaust temperature) for the preset time interval, and integrates the computed thermal energy over a time period between an ignition-on time and the current time. The integrated thermal energy is set to the load applied to the exhaust catalyst 61. The load applied to the exhaust catalyst 61 is reset in response to an ignition-off event. The high load range is an empirically specified high thermal energy range where forcible cooling of the exhaust catalyst 61 is required to lower the catalyst temperature than the specified temperature range causing deterioration of the catalyst.

When it is determined at step S320 that the load applied to the exhaust catalyst 61 is in the preset high load range, that is, when the stop condition of the engine 20 is satisfied and a high load is applied to the exhaust catalyst 61 under the fuel cut conditions and under the condition of the observed catalyst temperature in the specified temperature range causing deterioration of the catalyst, the engine ECU 50 idles the engine 20 to forcibly cool down the exhaust catalyst 61 by the flow of the relatively low-temperature exhaust gas (step S310) and exists from this engine control routine. The flow of the relatively low-temperature exhaust gas (for example, 500 to 600° C.) from the engine 20 into the exhaust catalyst 61 forcibly cools down the exhaust catalyst 61.

When it is determined at step S320 that the load applied to the exhaust catalyst 61 is out of the preset high load range, that is, when the stop condition of the engine 20 is satisfied but no high load is applied to the exhaust catalyst 61 under the fuel cut conditions and under the condition of the observed catalyst temperature in the specified temperature range causing deterioration of the catalyst, on the other hand, there is no need of forcibly cooling down the exhaust catalyst 61. The engine ECU 50 accordingly stops the rotations of the engine 20 (step S330) and exits from this engine control routine. Although the temperature of the exhaust catalyst 61 is in the specified temperature range causing deterioration of the catalyst, the air is not flown into the engine 20 to make the lean exhaust atmosphere in the non-idling state of the engine 20. The exhaust catalyst 61 is thus not exposed to the lean exhaust atmosphere and does not significantly deteriorate even at high temperature. The fuel injection from the injector 23 is stopped with the stop of the rotations of the engine 20. This desirably saves the fuel consumption and increases the fuel consumption rate.

After the engine stop, the engine ECU 50 restarts the engine 20 upon fulfillment of preset engine restart conditions. The engine restart conditions are fulfilled, for example, when the output powers of both the engine 20 and the motor MG2 are required to drive the wheels (for example, under acceleration) or when the low SOC of the battery 45 requires power generation of the motor MG1 to charge the battery 45. At the restart of the engine 20, the motor MG1 is controlled to crank the engine 20, while the fuel injected from the injector 23 is ignited with a spark of the spark plug 25.

In the control procedure of this embodiment, the engine ECU 50 stops the fuel injection from the injector 23 to cut the fuel when the catalyst temperature is out of the specified temperature range causing deterioration of the catalyst, under the fuel cut conditions. This arrangement stops the wasteful fuel injection under no requirement of the power of the engine 20 and accordingly increases the fuel consumption rate. The temperature of the exhaust catalyst 61 is lower than the specified temperature range causing deterioration of the catalyst. There is accordingly a low potential for deterioration of the exhaust catalyst 61 even in the idling state of the engine 20 to make the lean exhaust atmosphere.

As described above, when the stop condition of the engine 20 is satisfied during idling of the engine 20 under the catalyst deterioration control, the control procedure of the embodiment idles the engine 20 under application of a high load to the exhaust catalyst 61. The control procedure stops the rotations of the engine 20, on the other hand, under application of a low load to the exhaust catalyst 61. Under application of a high load to the exhaust catalyst 61, the relatively low-temperature exhaust gas from the engine 20 in the idling state forcibly cools down the exhaust catalyst 61. This prevents the exhaust catalyst 61 from being kept at high temperature. Under application of a low load to the exhaust catalyst 61, on the other hand, the stop of the engine 20 cuts off the air flow through the exhaust catalyst 61. The exhaust catalyst 61 is thus not exposed to the lean exhaust atmosphere and does not significantly deteriorate even at high temperature. This arrangement desirably achieves a good balance between prevention of significant deterioration of the exhaust catalyst 61 and the improved fuel consumption rate by the engine stop.

The prior art technique does not stop the engine 20 but keeps the engine 20 at idle, even when the stop condition of the engine 20 is satisfied under catalyst deterioration control. The control procedure of the embodiment, however, stops the engine 20 according to the level of the load applied to the exhaust catalyst 61. This arrangement desirably takes advantage of the characteristics of the hybrid vehicle 10 that automatically stops and restarts the engine 20.

The load applied to the exhaust catalyst 61 is determined according to the thermal energy of the exhaust gas, which depends upon the exhaust gas temperature and the exhaust gas flow. The concrete procedure determines the difference between the observed catalyst temperature and the observed exhaust gas temperature and the exhaust gas flow at every preset time interval, computes the thermal energy applied to the exhaust catalyst 61 for the preset time interval, and integrates the computed thermal energy over a time period between an ignition-on time and the current time. The integrated thermal energy is set to the load applied to the exhaust catalyst 61. This ensures adequate determination of the load applied to the exhaust catalyst 61.

Setting the rotational resistance of the rotor in the motor MG1 to zero causes idle rotation of the sun gear shaft 31 a and disconnects the engine 20 from the ring gear shaft 32 a (this is equivalent to the neutral gear position). The engine 20 thus readily shifts to a non-load operation or independent operation.

The embodiment discussed above is to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention.

The procedure of the embodiment determines the difference between the observed catalyst temperature and the observed exhaust gas temperature and the exhaust gas flow at every preset time interval, computes the thermal energy applied to the exhaust catalyst 61 for the preset time interval, and integrates the computed thermal energy over a time period between an ignition-on time and the current time. The integrated thermal energy is set to the load applied to the exhaust catalyst 61. One possible modification may set the starting point of integration to a preset time before the current time (for example, before several seconds to several minutes), instead of the ignition-on time. The observed catalyst temperature or the estimated catalyst temperature may be regarded as the load applied to the exhaust catalyst 61. In this case, for example, a modified procedure determines that the load applied to the exhaust catalyst 61 is in a preset high load range when the temperature of the exhaust catalyst 61 measured by the catalyst temperature sensor 63 is not lower than a predetermined threshold value (for example, 850° C.), which is higher than the lower limit (for example, 750° C.) of the specified temperature range causing deterioration of the catalyst. The modified procedure determines that the load applied to the exhaust catalyst 61 is out of the preset high load range when the observed temperature of the exhaust catalyst 61 is lower than the predetermined threshold value. The observed exhaust gas temperature or the estimated exhaust gas temperature may otherwise be regarded as the load applied to the exhaust catalyst 61. The observed exhaust gas flow or the estimated exhaust gas flow may also be regarded as the load applied to the exhaust catalyst 61. In such modifications, the procedure empirically sets a reference exhaust gas temperature or a reference exhaust gas flow in relation to a preset high load range and determines the level of the load applied to the exhaust catalyst 61, based on the exhaust gas temperature or the exhaust gas flow in or out of the preset high load range.

In the embodiment discussed above, the engine control routine of FIG. 7 is executed on the premise that the target torque Te* of the engine 20 is equal to 0, that the observed catalyst temperature is in the specified temperature range causing deterioration of the catalyst, and that the engine 20 runs idle without a fuel cut regardless of fulfillment of the preset fuel cut conditions. Namely the engine control routine of FIG. 7 is executed under catalyst deterioration control. The engine control routine of FIG. 7 may be executed on the only premise that the target torque Te* of the engine 20 is equal to 0. In this modification, under application of a high load to the exhaust catalyst 61, the relatively low-temperature exhaust gas from the engine 20 in the idling state forcibly cools down the exhaust catalyst 61. This prevents the exhaust catalyst 61 from being kept at high temperature. Under application of a low load to the exhaust catalyst 61, on the other hand, the stop of the engine 20 cuts off the air flow through the exhaust catalyst 61. The exhaust catalyst 61 is thus not exposed to the lean exhaust atmosphere and does not significantly deteriorate even at high temperature. This arrangement desirably achieves a good balance between prevention of significant deterioration of the exhaust catalyst 61 and the improved fuel consumption rate by the engine stop.

In the structure of the embodiment, the catalyst temperature is directly measured by the catalyst temperature sensor 63 set in the catalyst bed. The catalyst temperature depends on the heat input from the exhaust gas and the heat output to the exhaust gas. The catalyst temperature may thus be calculated from measurements of an inlet temperature and an outlet temperature of the exhaust catalyst 61. Another modified procedure may experimentally or otherwise set a variation in catalyst temperature against specified parameters representing certain driving conditions and indirectly estimate the catalyst temperature from the observed driving conditions.

The above embodiment regards application of the electronic engine control device of the invention to the hybrid vehicle having the combination of the parallel configuration with the serial configuration. The technique of the invention is applicable to any hybrid vehicles under cooperative control of an engine and a motor, for example, to both parallel hybrid vehicles and series hybrid vehicles. The technique of the invention is not restricted to the hybrid vehicles but may also be adopted in vehicles under idle stop control, which stops an engine in response to a decrease in vehicle speed to substantially zero by the driver's depression of a brake pedal to a certain level at each short stop, for example, at a traffic light, during a drive. In this case, the engine stop conditions in the flowchart of FIG. 7 may be that the brake pedal position BP represents the driver's depression of the brake pedal to at least a preset level and that the vehicle speed is substantially equal to zero. The similar functions and effects to those described in the above embodiment are expected in the vehicles under such idle stop control.

In the embodiment discussed above, the power of the motor MG2 is output to the ring gear shaft 32 a. In one possible modification shown in FIG. 9, the power of the motor MG2 may be output to another axle (that is, an axle linked with wheels 119), which is different from an axle connected with the ring gear shaft 32 a (that is, an axle linked with the wheels 19).

In the embodiment discussed above, the power of the engine 20 is output via the power distribution integration mechanism 30 to the ring gear shaft 32 a functioning as the drive shaft linked with the drive wheels 19. In another possible modification of FIG. 10, the construction may have a pair-rotor motor 330, which has an inner rotor 332 connected with the crankshaft 27 of the engine 20 and an outer rotor 334 connected with the drive shaft for outputting the power to the drive wheels 19 and transmits part of the power output from the engine 20 to the drive shaft while converting the residual part of the power into electric power. 

1. An electronic engine control device that controls an engine, said electronic engine control device comprising: the engine that converts combustion energy produced by combustion of an air fuel mixture or a mixture of the air and a fuel into kinetic energy; an exhaust catalyst that purifies an exhaust gas from the engine; a fuel injection unit that injects the fuel into the engine; a catalyst deterioration control module that controls the fuel injection unit to keep fuel injection and idles the engine regardless of fulfillment of a preset fuel cut condition, when temperature of the exhaust catalyst is in a specified temperature range causing deterioration of the catalyst; and an engine stop restart control module that stops the engine upon fulfillment of a preset engine stop condition and restarts the engine upon subsequent fulfillment of a preset engine restart condition, upon fulfillment of the preset engine stop condition during idling of the engine by said catalyst deterioration control module, said engine stop restart control module idling the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst.
 2. An electronic engine control device that controls an engine, said electronic engine control device comprising: the engine that converts combustion energy produced by combustion of an air fuel mixture or a mixture of the air and a fuel into kinetic energy; an exhaust catalyst that purifies an exhaust gas from the engine; and an engine stop restart control module that stops the engine upon fulfillment of a preset engine stop condition and restarts the engine upon subsequent fulfillment of a preset engine restart condition, upon fulfillment of the preset engine stop condition, said engine stop restart control module idling the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst.
 3. An electronic engine control device in accordance with claim 1, wherein said engine stop restart control module determines a level of load applied to the exhaust catalyst according to thermal energy of the exhaust gas.
 4. An electronic engine control device in accordance with claim 2, wherein said engine stop restart control module determines a level of load applied to the exhaust catalyst according to thermal energy of the exhaust gas.
 5. An electronic engine control device in accordance with claim 3, wherein said engine stop restart control module integrates the thermal energy of the exhaust gas over a time period to determine the level of load applied to the exhaust catalyst.
 6. An electronic engine control device in accordance with claim 4, wherein said engine stop restart control module integrates the thermal energy of the exhaust gas over a time period to determine the level of load applied to the exhaust catalyst.
 7. An electronic engine control device in accordance with claim 3, wherein said engine stop restart control module utilizes at least either of a temperature and a flow rate of the exhaust gas as the thermal energy of the exhaust gas.
 8. An electronic engine control device in accordance with claim 4, wherein said engine stop restart control module utilizes at least either of a temperature and a flow rate of the exhaust gas as the thermal energy of the exhaust gas.
 9. An electronic engine control device in accordance with claim 7, wherein an intake air flow introduced into the engine is set to the flow rate of the exhaust gas.
 10. An electronic engine control device in accordance with claim 8, wherein an intake air flow introduced into the engine is set to the flow rate of the exhaust gas.
 11. An electronic engine control device in accordance with claim 1, said electronic engine control device further comprising: a three shaft-type power input-output unit that determines a power input from and output to residual one shaft based on powers input from and output to any two shafts among three shafts, that is, an output shaft of the engine, a connection shaft connected to a first motor generator, and a drive shaft of a vehicle connected to a second motor generator, wherein the engine is idled by setting a rotational resistance of a rotor in the first motor generator to zero for an idle of the connection shaft.
 12. An electronic engine control device in accordance with claim 2, said electronic engine control device further comprising: a three shaft-type power input-output unit that determines a power input from and output to residual one shaft based on powers input from and output to any two shafts among three shafts, that is, an output shaft of the engine, a connection shaft connected to a first motor generator, and a drive shaft of a vehicle connected to a second motor generator, wherein the engine is idled by setting a rotational resistance of a rotor in the first motor generator to zero for an idle of the connection shaft.
 13. An electronic engine control device in accordance with claim 1, wherein the preset engine stop condition includes a condition that a current vehicle speed is in a preset engine stop permission vehicle speed range.
 14. A vehicle equipped with an electronic engine control device in accordance with claim
 1. 15. An electronic engine control method that controls an engine, said electronic engine control method comprising the steps of: (a) keeping fuel injection and idling the engine regardless of fulfillment of a preset fuel cut condition, when temperature of an exhaust catalyst, which purifies an exhaust gas from the engine, is in a specified temperature range causing deterioration of the catalyst; (b) upon fulfillment of a preset engine stop condition during idling of the engine in step (a), idling the engine under application of a high load to the exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst; and (c) restarting the engine upon fulfillment of a preset engine restart condition after stop of the engine in step (b).
 16. An electronic engine control method that controls an engine, said electronic engine control method comprising the steps of: (a) upon fulfillment of a preset engine stop condition, idling the engine under application of a high load to an exhaust catalyst, while stopping the engine under application of a low load to the exhaust catalyst; and (b) restarting the engine upon fulfillment of a preset engine restart condition after stop of the engine in step (a) 